Chromogenic and fluorogenic reagents for detecting compounds having one or more amine functionalities have a wide range of uses. Examples of such uses include detection and quantitation of peptides, amines, amino sugars, or amino acids in solutions and on surfaces. Thus, these reagents are useful for performance of biochemical assays and detection of latent fingerprints, among other applications.
Owing to the importance of latent fingerprint development and identification, forensic scientists have synthesized and employed a variety of reagents for amino acid detection on solid surfaces. Fingerprint identification reagents ideally exhibit high selectivity for amine compounds compared with other components of fingerprints, high sensitivity so that minute amounts of amine compounds may be detected, and sharp line resolution so that fingerprint patterns may be identified. In addition, such reagents are ideally easy to apply to surfaces, require no secondary treatment, and can be synthesized at low cost.
Fingerprints are among the most important forms of physical evidence found at crime scenes and can permit the unquestionable identification of an individual. The ridge patterns on the fingers of humans are unique, substantially immutable, and easy to classify. However, fingerprints deposited on surfaces are seldom visible. Fingerprints comprise glandular secretions including amino acids, urea, fatty acids, glycerides, inorganic salts, and the like. These components are not ordinarily visible and do not display significant inherent absorbance or fluorescence in the visible region of the electromagnetic spectrum.
A typical fingerprint comprises about one microgram of organic and inorganic compounds, including from about 100 to about 250 nanograms of amine compounds such as amino acids. Of course, the amount of material deposited on a surface may vary considerably, depending on such factors as glandular activity and the pressure applied to the surface when the fingerprint is deposited. Highly sensitive methods are therefore necessary for detection of latent fingerprints. Chemical methods of fingerprint detection have been demonstrated to be more effective than optical, physical, or physico-chemical methods for detection of fingerprints deposited on porous surfaces such as wood or paper (Margot et al., 1993, In: Manual of Fingerprint Detection Techniques, 5th ed. University of Lausanne, Lausanne, Switzerland, p. 109).
The capacity of ninhydrin to react with amine compounds to yield a colored product makes it a useful reagent for detection of amino acids such as those present in latent fingerprints (Ruhemann, 1910, Trans. Chem. Soc. 97:1438-1449; Ruhemann, 1910, Trans. Chem. Soc. 97:2025-2031; Oden et al., 1954, Nature 173:449). Secondary treatment using zinc salts has been demonstrated to enhance the sensitivity of the ninhydrin method of detecting latent fingerprints (Herod, 1982, J. Forensic Sci. 27:513-518). Other compounds useful for visualizing the amino acids present in latent fingerprints have been described, including 1,8-diazafluoren-9-one (DFO; Grigg et al., 1990, Tetrahedron Lett. 31:7215-7218), silver nitrate, chloronitrobenzoxadiazole, o-phthalaldehyde, p-dimethylaminocinnamaldehyde, benzoylquinolinecarboxaldehyde, fluorescamine, dansyl chloride, and the like. The chemical structures of several of these compounds are depicted in FIG. 1. However, each of these reagents have particular disadvantages, as described (Margot et al., In: Manual of Fingerprint Detection Techniques, 5th ed. University of Lausanne, Lausanne, Switzerland, p. 109; Baeyens et al., 1991, In: Luminescence Techniques in Chemical and Biochemical Analysis, Practical Spectroscopy Series, vol. 12, Brame, ed. Marcel Dekker, Inc., New York, p. 654).
The most sensitive and widely used reagents for latent fingerprint detection are ninhydrin and DFO. Although ninhydrin is an excellent chromogenic compound, a print developed with ninhydrin fluoresces only after a secondary treatment with zinc chloride. Forensic investigators regard the secondary zinc chloride treatment as a significant drawback. Development of a fingerprint using DFO does not require secondary treatment and has superior fluorogenic properties relative to ninhydrin. However, the cost of DFO is prohibitive for most crime laboratories. Hence, there remains a significant need for a fingerprint detection reagent which has fluorogenic properties equivalent or superior to those of DFO, but is less expensive to synthesize. The present invention satisfies this need.